Recently, the field of printed electronic application, especially the fabrication of electronic devices based on thin film technology, has drawn immense attention and due to this growing interest, a significant progress has been made in the micro fabrication field using a variety of patterning techniques. Assembling of components for molecular electronics, bioelectronics, and plastic electronics requires gentle lithographic techniques which guarantee the structural and functional integrity of the active building blocks. The so far known disruptive techniques such as evaporation of solids, sputtering, or ion etching generate defective structures in an uncontrolled way (1) (2). Soft lithography techniques (3), based on printing with polymer stamps, are gaining importance since they facilitate the transfer of molecular units and inorganic components at gentle conditions. Several printing approaches have been used so far for transferring metal films/electrodes onto various dielectric or semiconducting material substrates (2) (4) (5) (6) (7) (8). All these techniques require strong adhesion between the substrate and the transferred material. In most cases, however, the adhesion of the starting materials is weak and this may affect the performance of the final device.
Another approach to apply a metal material onto a solid is via linker chemistry. However, the binding chemistry of linker molecules to one solid may interfere with the binding chemistry to the second solid or materials on them. Currently used linker molecules do not provide exclusive binding selectivity for the metal to be transferred. These linker molecules suffer under a lack of versatility to chemically integrate functional (bio-) molecules into electrical (sensing) junctions.
Since the prior art methods are not satisfactory, the present inventors recognized an urgent need to provide a method how metals, preferably group Ib metals such as gold (Au) or copper (Cu), adhere strongly to other metal, isolator or semiconductor surfaces (e.g. SiO2). This method should avoid the generation of defective structures as often recognized with the prior art methods, should be fast and easy to perform and provide high yield products.
In this regard, the inventors have recognized that the surface properties of both the substrate and the metal need to be modified by the introduction of functional groups to overcome the barrier of weak adhesion between the solids and to increase the bonding capacity between them. Surface corrugations have to be compensated in order to provide conformal contact between the solids.